This article's title is uncanonical and a fan created one, because an official term or name has not been made yet.

The Battle of Hathsin was a seminal moment in the history of the cosmere, occurring near the cavern system containing the Pits of Hathsin and Kandra Homeland on Scadrial.[1] It was the culmination of the slow war of attrition between the intents of the ShardsPreservation and Ruin. It resulted in the near-destruction of Scadrial, the consumption of most of the world's atium, and the subsequent remaking of the planet by Sazed during the Catacendre. It also resulted in the deaths of Elend, Vin, Ati, and many other people.

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In the early stages of life on Scadrial, Leras, the Vessel of Preservation, struck a deal with Ati, the Vessel of Ruin: that while Preservation could create humanity, a species with sentience and more Preservation than Ruin within itself, Ruin would eventually be able to destroy the world. The creation of humanity expended a portion of Preservation's power, giving Ruin a slight advantage and breaking the balance of the two powers. This imbalance, however small, would allow Ruin to gradually make good on their deal. However, Preservation could not allow his creations to be destroyed and broke the deal, imprisoning Ruin's mind and drastically limiting his ability to influence the world at the cost of Preservation's own.

After the Siege of Fadrex City, and Vin's realization of Ruin's desire for atium - a portion of his power hidden from him by the Lord Ruler, she took off towards Luthadel in a feign to draw his attention, claiming that they had already found the cache. Ruin sent all of his Inquisitors after Vin, to stop her and capture the cache, but soon realized her trick as she fought the Inquisitors over Kredik Shaw. However, Marsh, desperately holding on to a portion of his sanity under Ruin's influence, is aided by Kelsier, who has partial control of Preservation's power, is finally able to momentarily buck the control of Ruin, pushing out Vin's earring and allowing her to finally consume the mists and draw in all of Preservation's power, defeating the Inquisitors and Ascending.

Shortly following Vin's Ascension, the coup, led by KanPaar, inadvertently reveals the true location of the Lord Ruler's atium cache: the Trustwarren. Located adjacent to the Pits of Hathsin, the Lord Ruler had cleverly hidden away the majority of the Atium mined there in a metal enclosed room within the kandra homeland. Ruin immediately tried to claim the kandra though their hemalurgicBlessings, but the vast majority of the kandra population carried out the Resolution of their First Contract, removing their blessings and Ruin's hold over their population, sacrificing their sentience and reverting to mistwraiths. However, a few rebellious kandra remained, and Sazed is able to pen them within the Trustwarren just log enough for Elend to arrive, guided by Vin and the trail of the Mistfallen soldiers he had sent to Luthadel.

Not to be deterred, Ruin sends his army of several hundred thousand koloss to assault the Pits, only for Elend to realize that his Mistfallen battalion are all Seers, mistings capable of burning atium. With a constant supply of atium dredged out by Sazed and other survivors, they fight spectacularly against seemingly endless waves of koloss. But in the end their metal reserves begin to dwindle, and they start to fall, one-by-one. Marsh then arrives from Luthadel, dueling with an exhausted and drained Elend, who soon fights only via an infusion of Vin's power. Ruin, through Marsh, taunts Elend, gloating over his impending victory, when Elend reveals their true purpose has been fulfilled: Burning away all of the atium that was stored within the Trustwarren. Marsh beheads Elend in a final outburst of anger and hacks apart his body. Demoux, one of the few surviving Mistfallen, retreats to the entrance of the caves, watching with Sazed.

However, Elend's death leaves Vin no reason to continue living and gives her the motivation to assault Ruin with the full force of Preservation. Her new status as a Vessel allows her to ignore the Shard's intent to preserve, and she gives up her life to assure their mutual destruction. As the powers falter, the koloss are left without direction and turn on one another, effectively ending the battle.

After the conflict, Vin and Ati's bodies fall to the ground near Elend, and Sazed runs forward to find their lifeless bodies. In his grief, he comes to a sudden realization, taking the power of the Shards leaking from their bodies, becoming Harmony, and fulfilling the prophecies of the Hero of Ages, initiating the Catacendre.[2]

Kelsier, who has been observing the battle from the Cognitive Realm, encounters the souls of Elend, Vin, and Ati after their deaths.[3]